[rpedela]

I think upfront is better because you should be charging based on value. So what if something only takes you a few hours. If it generates enormous value for the client then you should capture a percentage of that value regardless of the cost to you. Likewise, if you underestimate then yes you eat the cost but you have a much happier client in the long-term. They don't feel cheated when you tell them it will take X more time, and you don't have to waste your time on time tracking and emails about why something takes 30 minutes.

I also try not to give estimates to clients. Rather I ask when their deadline is. If they have none, then I say I will give weekly updates.